Helping people with computers... one answer at a time.
Flash memory is not the same as the type of memory used as your system RAM. They have different characteristics and they're accessed differently.
Can I use a USB RAM stick to increase system memory?
That was simple. But to avoid this becoming the shortest Ask Leo! article ever, let me explain why.
As you can probably guess by now, all memory is not created equal. Your system memory typically resides on your computer's motherboard, and uses a very high speed interface to connect to your computer's CPU. In fact, as fast as that interface is, it's still not as fast as we would like it (so true about so many things), and most modern CPUs actually copy or "cache" blocks of memory internally where they can access it even faster.
One of the characteristics of system memory is that when you remove power, *poof*, the memory has lost whatever it contained. Time to reboot.
USB Memory Sticks, on the other hand, are expected to retain whatever you put in them when the power is removed. Heck, they're expected to retain their memory when they're completely removed from the computer. As a result they use a different memory technology typically called "flash ram", which does exactly that. It's called "flash" because the memory contents are loaded, and then a special signal is sent that, in a sense, tells the memory to "remember this, now". It's kind of like taking a picture with a flash on your camera ... the picture "remembers" the state of everything when the flash went off. Flash BIOS is called that for the same reason - it's just flash memory that contains your computer's BIOS.
The downside to flash RAM is that it's slower. Reading flash memory is slower, and writing to flash memory is MUCH slower. It works fine as a virtual disk drive because our expectations for a disk's speed are quite different than what we expect for system memory.
In addition to the issue of the memory's own speed, there's also the USB interface to consider. As fast as it is for other purposes, it, too, is significantly slower than your system's main memory.
So USB RAM sticks, memory sticks, key chain drives, geek sticks, whatever you call them, are great for portable data storage. But increasing your system's memory is an entirely different proposition.